Methods and systems for lactic acid production and polylactic acid recycling

A method for producing an L-lactate salt from a combined recycling of polylactic acid (PLA) and organic waste, the method comprising the steps of:

• (a) hydrolyzing PLA waste with a metal oxide or a hydroxide to obtain a PLA hydrolysis slurry comprising L-lactate monomers and a first counterion;
• (b) fermenting organic waste with a lactic acid-producing microorganism in a fermenter in the presence of an alkaline compound to obtain a fermentation broth comprising L-lactate monomers and a second counterion,
• wherein the first and second counterions are the same;
• or wherein at least one of the first and second counterions is subjected to ion exchange thereby obtaining a first and second counterions which are the same;
• (c) optionally contacting the PLA hydrolysis slurry of step (a), the fermentation broth of step (b), or a mixture comprising the PLA hydrolysis slurry of step (a) and the fermentation broth of step (b) with a D-lactic acid degrading enzyme or a D-lactic acid-utilizing microorganism to eliminate D-lactate monomers thereby obtaining L-lactate monomers;
• and
• (d) purifying a mixture comprising the PLA hydrolysis slurry of step (a) and the fermentation broth of step (b) or the L-lactate monomers of step (c) thereby obtaining an L-lactate salt.

A method for producing magnesium L-lactate salt by recycling of polylactic acid (PLA) waste, the method comprising the steps of:

• (a) hydrolyzing PLA waste with a base selected from sodium, potassium and ammonium hydroxide to obtain a PLA hydrolysis slurry comprising L-lactate monomers and a counterion selected from sodium, potassium and ammonium;
• (b) optionally performing at least one of neutralizing the PLA hydrolysis slurry with an acid and removing unhydrolyzed PLA waste;
• and
• (c) adding a magnesium salt to the PLA hydrolysis slurry of step (a) or (b) to thereby precipitate magnesium L-lactate salt.